Drying of Wet Borax Pentahydrate by Microwave Heating

Kocakusak, S.; Köroglu, H. J.; Gözmen, T.; Savaşçı, Ömer Tunç; Tolun, R.

doi:10.1021/ie950119u

Cited by 10 publications

(5 citation statements)

References 5 publications

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“…Part of the difficulty may well be due to the fact that in this density region, one needs to avoid the glass transition resulting from the polymorphic degeneracy in the energy-density diagram. The second [28], much more recent, reports an hexagonal phase of density 0.69 g.cm −3 , incorrectly assigned to B 2 O 3 -I and which could well be one of our very low density polymorphs (< 0.7 g.cm −3 , Fig. 3a).…”

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confidence: 76%

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Hidden polymorphs drive vitrification in B2O3

Ferlat

Seitsonen²,

Lazzeri³

et al. 2012

Nature Mater

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Understanding the conditions which favor crystallisation or vitrification of liquids has been a long-standing scientific problem [1][2][3]. Another connected, and not yet well understood question is the relationship between the glassy and the various possible crystalline forms a system may adopt [4,5]. In this context, B2O3 is a puzzling case of study since i) it is one of the best glass-forming systems despite an apparent lack of lowpressure polymorphism ii) it vitrifies in a glassy form abnormally different from the only known crystalline phase at ambient pressure [6] iii) it never crystallises from the melt unless pressure is applied, an intriguing behaviour known as the crystallisation anomaly [7][8][9]. Here, by means of ab-initio calculations, we discover the existence of novel B2O3 crystalline polymorphs with structural properties similar to the glass and formation energies comparable to the known ambient crystal. The resulting configurational degeneracy drives the system vitrification at ambient pressure. The degeneracy is lifted under pressure, unveiling the origin of the crystallisation anomaly. This work reconciles the behaviour of B2O3 with that from other glassy systems and reaffirms the role played by polymorphism in a system's ability to vitrify [10,11]. Some of the predicted crystals are cage-like materials entirely made of three-fold rings, opening new perspectives for the synthesis of boron-based nanoporous materials. PACS numbers:Polymorphism, the possibility for a substance to form several distinct crystalline phases of identical composition, is observed for a wide range of materials. This phenomenon has tremendous importance not only per se for understanding the crystallisation process but also because of practical implications such as the design and control of new materials with specific properties [12], a major issue for the pharmaceutical industry [13]. Indeed, the ability of molecular units to pack in various ways generates crystal phases which generally differ in their physical properties and cohesive energies. Another important implication of polymorphism is related to the glassy state: as pointed out earlier [10,11], glass formation is often prevalent for those materials which are found in a variety of crystalline forms. An obvious example is silica (SiO 2 ), the archetypal glass-former, which at low pressure is found as quartz, cristobalite, keatite, tridymite, coesite and moganite [14]. The existence of these many polytypes illustrate that the structural units, here the SiO 4 tetrahedra, can occur in several conformations with little difference in strain energy, allowing for the possibility of metastable states [14]. The ease of glass formation is usually understood as the result of the system frustration associated to the presence of many minima of comparable energy in the crystal energy landscape (CEL). In the context of organic chemistry, it has also been observed that systems with many almost equi-energetic structures containing a common interchangeable motif, correlate with a t...

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confidence: 76%

“…Of course, kinetical or experimental difficulties may however prevent their observation. We note that there are at least two reports in the literature of low density polymorphs [27,28], both obtained by dehydration of H 3 BO 3 . In the first one [27], made in the early attempts to obtain B 2 O 3 -I, the structure is a cubic phase of density 1.805 g.cm −3 .…”

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confidence: 85%

Hidden polymorphs drive vitrification in B2O3

Ferlat

Seitsonen²,

Lazzeri³

et al. 2012

Nature Mater

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“…However, drying under reduced pressure becomes even more challenging due to ineffective convection in many cases. The problem of heat transfer may be solved by introducing microwave dielectric heating. − …”

Section: Introductionmentioning

confidence: 99%

“…The problem of heat transfer may be solved by introducing microwave dielectric heating. [28][29][30][31][32][33][34] The present paper deals with microwave-assisted vacuum drying of two pharmaceutical intermediates, based on earlier work, 35 and of a coenzyme of vitamin B 1 with different thermosensitivities, see Figure 1. The first one, N-acetylindoline-2-carboxylic acid, precipitated (1a) and nonprecipitated (1b), an intermediate in the synthesis of perindopril (an ACE inhibitor drug working to lower blood pressure), 36,37 is a relatively thermostable substance.…”

Section: Introductionmentioning

confidence: 99%

A Facile Microwave-Mediated Drying Process of Thermally Unstable / Labile Products

Pinchukova

Voloshko

Shyshkin

et al. 2010

Org. Process Res. Dev.

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The drying behavior of (S)-N-acetylindoline-2-carboxylic acid, precipitated (1a, 17 wt %) and nonprecipitated (1b, 5 wt %), and N-acetyl-(S)-phenylalanine ((S)-2-acetamido-3-phenylpropanoic acid, 2), both pharmaceutical intermediates, and of cocarboxylase hydrochloride (thiamine pyrophosphate, 3), a coenzyme, a bioactive form of vitamin B 1 , being a thermolabile substance, has been determined in straightforward drying setups. The method of supplying energy to the system had a profound influence on the drying rate and on the internal temperature of the samples during drying. The drying time of (S)-N-acetylindoline-2-carboxylic acid (1b) with the low moisture content (5 wt %) could be reduced by a factor 4 using microwave irradiation instead of conventional heating, while keeping the sample temperature under 35 °C. N-Acetyl-(S)-phenylalanine(2) with a higher moisture content (22 wt %) demonstrated a decrease in drying time by a factor 2.5 to 4 depending on the applied microwave powers. A reduction in drying time of the precipitated (S)-N-acetylindoline-2-carboxylic acid (1a, 17 wt % moisture) by a factor 2 was demonstrated for drying at 150 W of microwave irradiation instead of using a water bath at 70 °C. A dramatically shorter drying time by a factor 10 was found for cocarboxylase hydrochloride (3, 15 wt % water) on lab-scale which could be reproduced on pilot-plant scale. To achieve with conventional heating similar drying times as under microwave irradiation for the four examples, extremely high energy inputs should be applied, necessitating extremely high temperature differences between the heating source and the sample. The results reveal that microwave irradiation is less energy-consuming and is particularly useful for effective drying of thermally unstable materials in short periods of time.

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“…Microwave drying can, in that case, have an advantage over conventional hot air drying because of the direct effect on water molecules inside the material and consecutively bypassing the surface-to-center conduction stage. Microwave drying has been extensively studied in various applications, including drying of silica sludge, borax, and cotton, and in particular in food processing. − …”

Section: Introductionmentioning

confidence: 99%

Microwave Drying of Expanded Perlite Insulation Board

Skubic

Lakner

Plazl

2012

Ind. Eng. Chem. Res.

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The microwave drying process intensification of new inorganic thermal insulation board, containing expanded perlite and inorganic binder, was investigated in a multimode microwave applicator, with a 1.8 kW, 2.45 GHz microwave source. Ability to generate heat inside moistened material and to avoid the problem of heat conduction to the core of the material is especially important when dealing with efficient thermal insulators. A 3D unsteady mathematical model was developed, considering Lambert's law of exponential decay of microwave energy and nonuniform power distribution inside the microwave cavity, for temperature and drying rate predictions. The predicted temperature profiles at critical locations of the exposed board and cumulative drying rate were compared and verified with experimental data.

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Drying of Wet Borax Pentahydrate by Microwave Heating

Cited by 10 publications

References 5 publications

Hidden polymorphs drive vitrification in B2O3

Hidden polymorphs drive vitrification in B2O3

A Facile Microwave-Mediated Drying Process of Thermally Unstable / Labile Products

Microwave Drying of Expanded Perlite Insulation Board

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